Air conditioning systems for residential buildings, having heating and/or cooling and/or humidifying and/or dehumidifying and/or air-cleaning modes, for conditioning air, normally operate the system air distribution fan only when the air conditioning system is operating to condition air. Alternatively, the air distribution fan of an air conditioning system can be operated constantly. However, such a constant running of the fan would constitute a waste of energy and power, and could cause moisture related problems in warm, humid climates.
In air conditioning systems, a heating and/or cooling and/or humidifying and/or dehumidifying and/or air-cleaning apparatus produces conditioned air. Normally, the conditioned air is distributed by a fan or blower through various ducts throughout an interior space in order to place the conditioned air at desirable locations. Generally, thermostats or humidistats are used to activate the conditioning apparatus. For example, when the air temperature within an interior space drops below a selected level, an air temperature sensor and switch in a thermostat can activate a heating apparatus and an air distribution fan. Likewise, when the air temperature within an interior space rises above a selected level, an air temperature sensor and switch in a thermostat can activate a cooling apparatus and an air distribution fan. Likewise, when the air humidity within an interior space drops below a selected level, an air humidity sensor and switch in a humidistat can activate a humidifying apparatus and an air distribution fan. Likewise, when the air humidity within an interior space rises above a selected level, an air humidity sensor and switch in a humidistat can activate a dehumidifying apparatus and an air distribution fan. The conditioning apparatus and air distribution fan are deactivated when the interior space temperature or humidity reaches the selected level. In some air conditioning systems, while in the heating mode, the air distribution fan may continue to run after the heating apparatus has been deactivated, usually until residual heat in the heating apparatus has been removed by the circulating air. Likewise, in some air conditioning systems, while in the cooling mode, the air distribution fan may continue to run after the cooling apparatus has been deactivated, usually for a preset delay time to continue to distribute cool air while the cooling apparatus is still cold. In warm, humid climates, this running of the air distribution fan immediately after the cooling/dehumidifying apparatus has been deactivated is counter-productive, in that, moisture on the wet cooling/dehumidifying apparatus is returned to the interior space by the circulating air. However, no known control systems exist having means to periodically operate the air distribution fan for a first selectable time period after a second selectable time period from the end of the last operation of the air distribution fan, that is, operate the fan dependent on the last operation of the fan.
Prior art related to the air distribution fan recycling control portion of the present invention is cited but was not found to overcome the problems cited above. See for example, U.S. Pat. Nos. 2,882,383 to Boyd Jr. et al.; 3,454,078 to Elwart; 4,167,966 to Freeman; 4,267,967 to Beck et al.; 4,452,391 to Chow; 4,718,021 to Timblin; 4,773,587 to Lipman; 5,131,236 to Wruck et al.; 5,179,524 to Parker et al.; 5,325,286 to Weng et al.; and Japanese Patents 0095538 and 0008544. U.S. Pat. No. 4,838,482 to Vogelzang describes an air conditioning system with periodic fan operation. However, this device is limited to periodic cycling of the air distribution fan during periods when the activation of a heating or cooling apparatus has been locked out. Vogelzang '482 describes a fan cycle mode, selected on a thermostat, that energizes a switch that turns the fan on and off a "predetermined number of times each hour" such as "6" times per hour. When this fan cycle mode is selected, the heating or cooling modes cannot be activated, since the operation of the heating and cooling apparatus require non-cycling, constant, operation of the air distribution fan. If operation of the heating or cooling apparatus is desired, the fan cycling mode must be manually de-selected. The Vogelzang '482 fan cycling system is not dependent upon the last operation of the fan nor dependent on the last operation of the heating or cooling apparatus. In fact, Vogelzang '482 specifically claims that the fan cycling is "independent" of the operation of the heating or cooling apparatus. Whereas, prior U.S. Pat. No. 5,547,017 to Rudd, the same inventor of the subject invention, requires recycling of the air conditioning system air distribution fan "where the periodic ON/OFF control of the fan is dependent on the time since the last fan operation." A signal from the thermostat to operate the heating or cooling or constant fan modes will automatically interrupt the fan recycling. Rudd '017 can determine the selectable time delay based on the volume dimensions of the rooms and/or the number of occupants.
In air conditioning systems, an outside air duct connecting between the outside of an interior space and the return air side of an air distribution fan, for the purpose of drawing in ventilation air, is known. Often, motorized dampers are placed in the outside air duct to limit outside air entry to times when the air distribution fan is operating. Motorized outside air dampers are known and exist commercially. It is known to energize an outside air damper upon energizing an air distribution fan, and it is known to de-energize a damper upon de-energizing an air distribution fan. However, no known control systems exist to first open an outside air damper upon energizing an air distribution fan, then for as long as the fan continues to operate, to periodically close and open the outside air damper based on selectable time periods since the outside air damper was last opened or closed, respectively, then to close the outside air damper at the end of each operation of the air distribution fan. In this way, the subject invention would control the outside air damper position dependent on the operating time of the air distribution fan, and allow a limit to be placed on the amount of outside air to be drawn in when the air distribution fan is operating.
Standards enacted in 1989 by the American Society of Heating, Refigeration and Air Conditioning Engineers (ASHRAE) such as the ASHRAE 62-89 Standard now require 15 cubic feet per minute of outside air per person in residential dwellings, which can result in approximately 0.35 air changes per hour. The ASHRAE 62-89 Standard further includes a recommendation to limit the concentration of carbon dioxide to 1000 parts per million to control indoor air quality due to respiration.
The Manufactured Home Construction and Safety Standards set forth by the U.S. Department of Housing and Urban Development (HUD) has enacted standards for manufactured homes that require fresh air ventilation systems. These ventilation systems must distribute outdoor air throughout the conditioned living space. Some ventilation systems require the installation of supply ducts separate from those of the air conditioning system, to distribute ventilation air. The separate ventilation supply ducts are potentially an unnecessary additional expense.